Lightweight firebrick and process of producing the same



Patented May 30, 1950 t aurwuionr m n cK-ANnmocEs a r'racw em m a-Qhieago, Ill assig-nor to Universal sillation mp n Ghicaco, 111- a e tba ib hetlilou en i No Drawing. ,ApplicationApril 115,619.47, 'iSeria'l N0. #741,686

This nven on t nere ia -we m ifirebricks an zt snmcesszfc r du iniheeeuie- Such fir b i kse e extensivel s d n ,struction of indust ialzi xnece alifili fi Running ,of athesame. The firebriclgs in -thesefluuaqcs are su j c ed to hi emp ratur s. a i i D fie :sary that they bestable agains breakdown in u s nce the nser thezl t i e ft i ,fl ehtiskth few r i t r unt usw l he pqc si esdsill-li s 9pc?- Insulatingfirebricks have, in recent years, been classifie in a number-9fereunsrrsl ed to h atemperature of maximum v se e to which the r k m y bs i l ubiectd in -creeps ar e al y num ric l des na ed as aiol ow Q ou6, a i .i r t t mperatu e up t Group Zoe-Satisfactory to temperatures upto The present invention is concernedwith firebricks produced fromexfoliated vermiculite and a binder of unique character under conditionsyielding a novel firebrick that is useable with remarkable satisfactionat-temperatures upto-21-00 F.--without appreciable shrinkage. A

It is recognized that glqentonitesbonded exfoliated vermiculite brickshave heretofore been produced. Such bentonite-bpnded exfoliatedyermiculite bricks are reasonably satisfactory in service up totemperatures of about 1800 F., but at, higher temperatures shrinkage,believed to be occasioned by incipientiusi-on o f the ,ver rniculite andthe ,bentonite binder, is so,greatesjtorender such bricks unuseable atthe higher temperatures.

By the present invention it is possible to produce firebricks comprisedof exfoliated vermiculite and the novel binder of this invention, whichbricks can be satisfactorily used at temperatures at least as high as2100 F. Thus} through the present invention, the field of use ofexfoliated vermiculite firebricks is very substantially expanded.

In carrying out the present invention, the exfoliated vermiculiteparticles employed in producing the firebricks should pass, aone-quarter inch opening, and at least 25%.should pass a mesh screen andno more than 20% should pass a 200 mesh screen.

a ion of the urnacetotemperatures up to glib H J20 h G oup ,2 at fia qrto em e atur p i ,2 The binder suitable for use in practicing thejnyentior i,is,know,n as hectorite. This clay mineral has been found innature near Hector, Cali- .fornia. It is described in some detail in theGeological.Survey Professional Paper 205,B, entitled Minerals of theMontmorillonite Group, Their Origin and Relation to Soils and Clays," by(llarences. Ross and Sterling B. Hendricks, publishedin 1945 andavailable through thesaperintendent of Documents, United States cernrnent Printing Ofiice. Hectorite maybe generally characterized as havingan fiiOz to MgO ratio of at least 2 .to 1, and an A120 contentllessthanrl%.

'lypicalanalyscs of samples of hectorite areas follows:

carbonate). The presence of calcite (calcium carbonate) crystals has nodeleterious efiect on the bonding power of themagnesium silicate of thehectorite, and appears to constitute no more than a diluentwhich doesnot depreciate the refractory character of the finished bricks. It isacco din ly perm ible and w in the, s p o t einr sent i ent on o m loyth he or t i admixture with calcite, andreference-in the subjoinedclaims to hectorite is not to be construed as exclusive of calcite.

By way of example, the process may be carried out in the followingmanner:

Seventy-five pounds of exfoliated vermiculite, all the particles ofwhich pass through a one-quarter inch opening and 40% of which pass a 30mesh screen, with only 7% passing a 200 mesh screen, are mixed with 25pounds of hectorite binder containing a minor portion of calcitecrystals, all of the binder being finely pulthe limits of from 15% to30% by weight of verized. The exfoliated vermiculite and the binder aredry mixed until a uniform admixture is obtained, which admixture can besecured in one or two minutes in the conventional rotary mixer. Water isthen added, preferably through sprays, and mixing continued until thewater is evenly distributed throughout the mix, which usually requiresnot more than three minutes additional time, making the production ofthe wet mix require not more than about five minutes. The amount ofwater should be maintained Having described my invention, what I claimis: 1. A dry mix suitable for use in the production of insulatingfirebrick and furnace linings comprising from 70% to 85% by weightexfoliated vermiculite"particleswhich pass a one-quarter inch opening,at least 25% by weight pass a 30 mesh screen and not more than 20% byweight pass a 200 mesh screen, and from to 30% by 2 weight of a, finelypulverized binder of hectorite,

7 characterized in that it has an S102 to MgO ratio within the limits of30% to 50% by Weight of v the dry ingredients, and preferably at about40% by weight of the dry ingredients when the bricks are to be formed byso-called dry pressing. The consistency of the above-described will beof at least 2 to 1 and an A1203 content less than found to be such thatin appearance it is dry but when subjected to pressure the mix will bondto- 2..' A process forproducing insulating firebrick comprising forminga mixture containing from 70% to'85 byweight of exfoliated vermiculiteparticles characterized in that they pass through I a one-quarter inchopening, at least 25% thereof gether. Any great excess of water causesthe mix to adhere to the dies of the brick press, andfurthermore makesthe mix gummy and requires a prolonged drying period. Theabove-described mix is pressed in a suitable mechanical press to formbricks. The pressure required is of the order of 25 pounds per squareinch. The pressed bricks ;are dried, preferably at a temperature of theorder of 300 to 490 F, to remove the water added during mixing. Afterthe bricks are thus dried, they are fired to a temperature between 1500?F. and 2000 F., during which firing a ceramic bond is formed between thebinder and the vermiculite.

Bricks produced in accordance with the foregoing process have been foundto withstand tem--,

peratures up to 2100 F. without appreciable shrinkage, and to fullycomply with the ASTM specifications for shrinkage of insulatingfirebricks. 'The commercial classification for bricks known as Group 20,i. e. the 2000 F. class, re-

quires that these bricks shink no more than 1 at' ,1950" F. The bricksproduced in accordance with the present invention meet this commercialclassification, whereas bricks of vermiculite composition heretoforeproduced have been relegated toa lower classification, since they havebeen incapable of meeting such specifications.

' While in the exemplified procedure by weight of the hectorite binderhas been illustrated, it will be appreciated that a greater quantity ofth'e binder can be employed and will yield somewhat greater strengthwith increased weight of the product. Lesser quantities of the bindercan be employed, but occasion a decrease in the strength of the product.It is accordingly recominende'd that the binder be employed within thedry mixture.

While the invention is primarily addressed to insulating firebricks andthe process of their manufacture, the dry mixture may be itself mar-'keted and mixed With water to be applied as a cement liner in structureswhere brick lining is impractical, and wherein the cement may be driedand fired in situ.

passing a 30 mesh screen and not more than 20% thereof passing a 200mesh screen, and from 15% to 30 by weight of a binder of hectorite char--acte'riz'ed' in'that' it' has a SiOz to MgO ratioof .3. An insulatingfirebrick capable of withstanding temperatures up to 2100 F. withoutappreciable shrinkage, comprised of from to %by weight of exfoliatedvermiculite particles,

which passa. one-quarter inch opening, at least 25% of which pass a 30mesh screen, and not more than 20% of which pass a 200 mesh screen, 'andfrom 15% to 30% by Weight of a binder of hectoritehaving an S102 to MgOratio of at least 2 to 1 and an A1203 content less than 1% by weight. 1

ROBERT F. REA.

" REFERENCES CITED 7 The following references are of record in the fileof this" patent:

,, 'UNITEnsTATEs PATENTS I Date Number W y'Name 2,079,665 "Sei-gle May11, 1937 2,215,078 Cavadino Sept. 17, 1940 v FOREIGN PATENTS Number 5Country Date 485,506 Great Britain 1938 OTHER REFERENCES Stern: Role ofClay and other Minerals in Oil-Well Drilling Fluids, page 58 (U. S.Bureau of Mines, Feb. 1941, Report of investigations, No. 3556).

1. A DRY MIX SUITABLE FOR USE IN THE PRODUCTION OF INSULATING FIREBRICKAND FURNACE LININGS COMPRISING FROM 70% TO 85% BY WEIGHT EXFOLIATEDVERMICULITE PARTICLES WHICH PASS A ONE-QUARTER INCH OPENING, AT LEAST25% BY WEIGHT PASS A 30 MESH SCREEN AND NOT MORE THAN 20% BY WEIGHT PASSA 200 MESH SCREEN, AND FROM 15% TO 30% BY WEIGHT OF A FINELY PULVERIZEDBINDER OF HECTORITE, CHARACTERIZED IN THAT IT HAS AN SIO2 TO MGO RATIOOF AT LEAST 2 TO 1 AND AN AL2O3 CONTENT LESS THAN 1% BY WEIGHT.